A recently proposed position detection apparatus based on magnetic field detection creates a resonance state in an LC resonant circuit disposed in a detection object by supplying a magnetic field, acquires a magnetic field newly generated by the resonance through a plurality of magnetic field sensors, and detects the position and orientation of the detection object from the acquired information (see, for example, Patent Document 1 and Non-patent Document 1).
In the technique described in Patent Document 1 above, the magnetic field strength detected by the sensors includes both the magnetic field strength of a magnetic field generated toward the LC resonant circuit and accidentally reaching the sensors (ambient magnetic field) and the magnetic field strength of a magnetic field generated from the LC resonant circuit and reaching the sensors as intended (resonant magnetic field).
To remove the magnetic field strength of the ambient magnetic field accidentally reaching the sensors, before the position of the detection object is measured, the magnetic field strength of the ambient magnetic field is measured with the LC resonant circuit removed from a detection space where the position of the detection object can be detected (calibration). Afterwards, the magnetic field strength of the ambient magnetic field and the resonant magnetic field is measured with the LC resonant circuit introduced into the detection space, and the difference between that magnetic field strength and the magnetic field strength of the ambient magnetic field measured in the above calibration is determined to remove the magnetic field strength of the ambient magnetic field and determine the magnetic field strength of the resonant magnetic field.
This allows only the resonant magnetic field created by the LC resonant circuit to be collected to accurately calculate the position of the detection object.
Patent Document 1:
Japanese Unexamined Patent Application, Publication No. 2006-26391
Non-patent Document 1:
Tokunaga, Hashi, Yabukami, Kohno, Toyoda, Ozawa, Okazaki, and Arai, “Precision Position-Detecting System using LC Resonant Magnetic Marker”, J. Magn. Soc. Jpn., Vol. 29, No. 2, pp. 153-156 (2005)